In recent years, more and more construction machines are electrified with the aim of, for example, improved engine fuel efficiency and reduced amounts of exhaust gases based on the techniques relating to hydraulic excavators. Examples of such construction machines include a hybrid construction machine that incorporates both a hydraulic actuator and an electric motor as actuators for driving different parts of the machine, in addition to an engine and an electric motor (a generator motor) as prime movers for a hydraulic pump. A known hybrid construction machine drives hydraulic actuators (hydraulic cylinders and hydraulic motors) to cause a work implement to perform work and a track structure to perform a traveling operation. It also drives an electric motor to cause a swing structure (e.g., an upper swing structure in a hydraulic excavator) to perform a swing operation.
The hybrid construction machine of the foregoing type may use a controller (e.g., an inverter device) for controlling the electric motor to achieve intended swing control by converting an operation amount of a swing operating lever operated by an operator to a corresponding electric signal and applying the electric signal to the controller. A fault that may occur in an electronic control system that includes a sensor for detecting a state of the electric motor (e.g., a magnetic pole position sensor of the electric motor), the controller, and the electric motor in a series of control processes, however, hampers correct swing control, resulting in a swing operation not intended by the operator being performed.
A known technique for avoiding such a situation as that described above uses a controller that monitors a difference between a speed command of an electric motor (a target speed) generated based on the operation amount of the swing operating lever and an actual speed of the electric motor and determines the operation to be a faulty operation when the difference falls outside a permissible range (see JP-A-2007-228721).